Unfortunately, future or past versions of the same character would still be considered duplicates -- even if in-canon time travel means they can be present at the same time/interact in canon. Because of that, with a Future Trunks in game, Kid Trunks can't be apped, and with a Kid Gohan in game, Future Gohan wouldn't be appable, because they're the same person at two different times in his life.
(Similarly, kid Anakin Skywalker and Darth Vader would be considered duplicates, for example. As a general guideline, if an age-up/age-down event could turn one character into the other, they couldn't both be in game at the same time.)
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Unfortunately, future or past versions of the same character would still be considered duplicates -- even if in-canon time travel means they can be present at the same time/interact in canon. Because of that, with a Future Trunks in game, Kid Trunks can't be apped, and with a Kid Gohan in game, Future Gohan wouldn't be appable, because they're the same person at two different times in his life.
(Similarly, kid Anakin Skywalker and Darth Vader would be considered duplicates, for example. As a general guideline, if an age-up/age-down event could turn one character into the other, they couldn't both be in game at the same time.)